The present invention relates to a variable displacement compressor for vehicle air-conditioning system. More specifically, the present invention relates to a variable displacement compressor having a drive plate for reciprocating pistons, the inclination angle of which is varied.
FIGS. 3 and 4 show a conventional variable displacement compressor. A drive shaft 102 is rotatably supported in a housing 101. The housing 101 includes cylinder bores 101a, a crank chamber 103, a suction chamber 104, and a discharge chamber 105. A piston 106 is accommodated in each cylinder bore 101a to reciprocate. A rotor 107 is fixed to the drive shaft 102 in the crank chamber 103. A drive plate, or a swash plate 108, is accommodated in the crank chamber 103. The drive shaft 102 penetrates the swash plate 108. A hinge mechanism 109 is located between the rotor 107 and the swash plate 108. The hinge mechanism 109 rotates the swash plate 108 together with the drive shaft 102 and the rotor 107 and permits the swash plate 108 to incline with respect to the drive shaft 102. The pistons 106 are coupled to the swash plate 108.
The drive shaft 102 is connected to an external drive source, or an engine 110, of the vehicle without a clutch mechanism such as an electromagnetic clutch. The drive shaft 102 is constantly driven while the engine 110 is running. The swash plate converts the rotation of the drive shaft 102 into reciprocation of each piston 106. Each piston 106 draws refrigerant gas from the suction chamber 104 to the corresponding cylinder bore 101a and compresses the gas. Then, the refrigerant gas is discharged from the cylinder bore 101a to the discharge chamber 105.
A pressurizing passage 111 connects the crank chamber 103 to the discharge chamber 105. A bleeding passage 112 connects the crank chamber 103 to the suction chamber 104. A displacement control valve 113 is located in the pressurizing passage 111. The control valve 113 is an electromagnetic valve and moves a valve body 113b by exciting and de-exciting a solenoid 113a. This opens and closes the pressurizing passage 111. When the solenoid 113a is excited, the control valve 113 closes the pressurizing passage 111. When the solenoid 113a is de-excited, the control valve 113 opens the pressurizing passage 111.
As shown in FIG. 3, when the pressurizing passage 111 is closed, the refrigerant gas does not flow from the discharge chamber 105 to the crank chamber 103. Accordingly, the pressure in the crank chamber 103 decreases and the inclination angle of the swash plate 108 increases. This increases the piston stroke and displacement of the compressor. As shown in FIG. 4, when the pressuring passage 111 is opened, the refrigerant gas flows from the discharge chamber 105 to the crank chamber 103. Accordingly, pressure in the crank chamber 103 increases and the inclination angle of the swash plate 108 decreases. This decreases the piston stroke and displacement of the compressor.
A suction passage 114 is formed in the housing 101 and connects an external refrigerant circuit to the suction chamber 104. A shutter 115 engages the rear end of the drive shaft 102 and slides along the axis of the drive shaft 102. The shutter 115 moves with the swash plate 108 and selectively opens and closes the suction passage 114. As shown in FIG. 3, when the swash plate 108 is positioned at its maximum inclination angle by the excitation of solenoid 113a, the shutter 115 opens the suction passage 114. Accordingly, the refrigerant gas flows from the external refrigerant circuit to the suction chamber 104. As shown in FIG. 4, when the swash plate 108 is positioned at its minimum inclination angle by the demagnetization of the solenoid 113a, the shutter 115 closes the suction 114. Accordingly, refrigerant gas does not flow from the external refrigerant circuit to the suction chamber 104. This stops the circulation of refrigerant gas between the external refrigerant circuit and the compressor.
The control valve 113 includes an electromagnetic valve and suddenly opens the pressurizing passage 111 when the solenoid 113a is demagnetized. Accordingly, high-pressure refrigerant gas of the discharge chamber 105 suddenly flows into the crank chamber. This suddenly increases pressure in the crank chamber 103 and reduces the inclination angle of the swash plate 108. This increases friction on the engaging parts of the hinge mechanism 109, the swash plate 108 and the drive shaft 102, which produces vibration and noise.